Process of preparing sensitive films for photographing in relief.



rrnn STAT S Fries,

ATENT PROCESS OF PREPARING SENSITIVE FILMS FOR PHOTOGRAPHING IN RELIEF.

SPECIFICATION forming part of Letters Patent No. es'aeso, dated October8, 1 eoi. Application filed Octhber 20, 1900. Serial No. 343L778. (Nospecimens.)

T0 to whom, it may concern:

Be it known that I, CARL PIETZNER, a subject of the Emperor ofAustria-Hungary, residing at Vienna, in the Empire of Austria- Hungary,have invented certain new and useful Improvements in Processes ofPreparing Sensitive Films for Photographing in Relief, of which thefollowing is a specification.

My invention has relation to a process of preparing sensitive films forrelief photography, and in such connection it relates more particularlyto the manner in which the film of bichromated gelatin is prepared priorto its exposure in printing to the negative or positive plate from whichthe reproduction in relief is to be taken.

As is well known in the art, fiat reliefs may be produced by exposing afilm of bichromated gelatin to the action of light passing through thenegative or positive plate to be reproduced and in fixing in a suitablemanner, as in a bath, the treated film. The results of such treatmentand action are unsatisfactory, mainly because the bichromated gelatinfilm is not supersensitive, and the long exposure, particularly in dampand cloudy weather, of the film results in its absorbing moisture andbecoming even less sensitive, and the reliefs obtained are very fiat.This susceptibility to variation under atmospheric changes and longexposure prevents good results being obtained from the film. In theBritish patent to Pretsch, No. 2,373, of 1854:, it is suggested that byadding silver-nitrate, with or without the addition of potassium bromid,to the composition from which the film is to be made the time ofexposure may be shortened. By the use of these auxiliaries, however,none but fiat plates are obtained, which are suitable for printing onlywhen a galvano-plastic copy thereof is made.

The principal object of my invention is to so modify and improve thePretsch process that the sensitiveness of the film may be increased fromten to even twenty fold and yet much higher and better modeled reliefsmay be produced. To carry my invention into effect, the bichromatedgelatin is mixed with silver nitrate, either with or Without theaddition of potassium bromid, and then to the mixture absolute alcoholis added and the mixture heated for a long time and then quickly cooled.

The technical advantages obtained by using films of high sensitivenessprepared accord ing to my invention are, first, the possibility ofreducing considerably the time of exposure, and, second, the possibilityof using a fixed artificial source of light, which results in obtaininggreater sharpness and graduation than are possible when the suns raysare used, since those rays do not always strike the plate at the sameconstant angle, and hence the lines are spread and accurate work isimpossible. The artificial light may be an electric or magnesium lightor even gas-light or Roentgen rays. The short exposure of the film underthe negative or positive, together with the fact that the film may nowbe exposed in a closed room at an even temperature, removes thepossibility of the film ab sorbing moisture from the surroundingatmosphere in such quantities as to impair se riously the sensitivenessof the film.

A further advantage of a film prepared according to my invention residesin the fact that the layers of the preparation'remain unchanged during along period of time and do not lose, even after months have passed,their essential properties of relief and reproduction of graduation.

To carry my method into effect, a normal solution is prepared,preferably as follows: To a liter of ordinary bichromated-gclatinsolution are added approximately twenty-five grams of silver nitrate.The mixture thus formed is then heated to about centigrade until thesolids have completely dissolved. There is then added, if required,twenty grams of potassium bromid or similar prepa ration, and themixture is slightly acidulated and permitted to stand in hot water forabout half an hour. To the solution is then added about one hundredgrams of absolute alcohol, and the mixture is then quickly cooled andthe preparation is ready for use. The preparation must be stored in thedark and'handled only in the presence of a red light. By varying theamount of silver nitrate or acid preparation added to the mixture aharder or softer relief may be obtained, the reduc tion of the amount ofsilver nitrate or acid for photographing in relief, which consists infirst adding silver nitrate to an acidulated solution of bichromatedgelatin, then heating the mixture for a lengthy period of time, thenadding absolute alcohol to the mixture, and finally cooling the mixturequickly.

In testimony whereof I have hereunto set my hand in presence of twosubscribing witnesses.

CARL PIETZNER.

Vitnesses:

O. B. Hunsr, ALVESTO S. Hoses.

